Synergistic Antibacterial Activity of Hyssopus officinalis L. Extracts with Standard Antibiotics Against Multidrug-Resistant Bacteria: An In Vitro Study

Background: Hyssopus officinalis L. (hyssop) is a traditional herb that already has established use, which implies inherent antimicrobial activity that would be applicable in the present crisis of antimicrobial resistance. Hypothesis: The purpose of the study was to identify the phytochemical composition, the antimicrobial action, and synergistic effect of the H. officinalis extracts in combination with standard antibiotics (Vancomycin and Erythromycin) to MDR clinical isolates (MRSA, E. coli and K. pneumoniae). Procedures: n-hexane, ethanol and ethyl acetate extracts were prepared. Initial phytochemical screening and total phenolic content (45 ug gallic acid equivalent/ml in the ethyl acetate fraction) was measured. Antibacterial activity was evaluated by broth micro dilution method (to find out the MIC) and the agar well diffusion method to evaluate the individual and combined treatments on the three bacterial strains. Findings: Polar extracts (ethanol and ethyl acetate) had great intrinsic activity with an MIC of 25 percent in all the isolates. The ethyl acetate extract as such had a significant inhibitory effect especially against MRSA (18 mm). More importantly, the extract had a synergistic effect with Vancomycin as it managed to regain its activity against a resistant MRSA and K. pneumoniae (producing up to 11 mm of inhibition zones). On the other hand, the extract was antagonistic in the presence of Erythromycin leading to total deactivation of the action of the drug on MRSA. Conclusion: Ethyl acetate extract of H. officinalis is an effective antimicrobial substance, and an effective antibiotic adjuvant. Its ability to revert the effects of Vancomycin on MDR pathogens justifies its possible use in combination therapy but additional mechanistic efforts are needed to better comprehend and overcome the observed antagonistic effects.